This invention relates to a process for the preparation of substituted haloaromatic compounds by dehydrogenation of a corresponding halogen substituted saturated or partially saturated cyclic compound. The substituted halobenzene compounds are useful chemical intermediates for the synthesis of various commercial products, including polymers, dyes, pharmaceuticals, and agricultural chemical products.
Processes for the preparation of aromatic compounds by dehydrogenation of hydroaromatic compounds are known in the literature. Thus, for example, U.S. Pat. No. 3,883,599 discloses the preparation of thiophenols by dehydrogenating the corresponding cyclohexyl mercaptan by heating in the vapor state with sulfur dioxide, in the presence of a catalyst such as activated carbon, alumina, or chromium oxide on alumina.
The use of various dehydrogenation catalysts, including selenium, sulfur, and palladium on charcoal, in the dehydrogenation of hydroaromatic compounds is described by Fieser and Fieser, Organic Chemistry. third ed., Heath, Boston, 1956, at page 545.
U.S. Pat. No. 4,560,772 discloses the reaction of 4-methyltetrahydrophthalic anhydride with excess sulfur and a catalytic amount of zinc oxide and 2-mercaptobenzothiazole to produce 4-methylphthalic anhydride and hydrogen sulfide.
U.S. Pat. No. 4,560,773 discloses a similar reaction between the electron rich 4-methyl-tetrahydrophthalic anhydride and bromine in the presence of an acid acceptor such as dimethylformamide or pyridine in the liquid phase.
U.S. Pat. No. 4,709,056 discloses the dehydrohalogenation of dihalohexahydrophthalic anhydrides through the use of a basic alumina catalyst in a liquid phase to produce 4-fluoro-1,2,3,6-tetrahydrophthalic anhydride.
Ohkatou et al., J. Jaoan Petrol. Inst., 22, 164-9 (1979) discloses the preparation of benzene by dehydrogenation of cyclohexane in the presence of activated carbon.
Bergmann J. Amer. Chem. Soc. 64, 176 (1942) discloses the aromatization of tetrahydrophthalic anhydride products of Diels-Alder reactions. The author discloses that dehydrogenation occurs when the tetrahydrophthalic anhydride product is boiled in nitrobenzene. However, it is further disclosed that dehydrogenation does not occur when p-bromonitrobenzene, p-chloronitrobenzene, or m-dinitrobenzene in xylene is employed.
U.S. Pat. No. 4,517,372 to Tang, disclose a process for the preparation of 4-fluorophthalic anhydride by dehydrogenation of gem-, difluoro- or gem-chloro-fluoro- hexahydrophthalic anhydrides in the presence of a dehydrogenation catalyst, such as palladium.
U.S. Pat. No. 4,709,056 to Cotter, Lin, and Pawlak discloses the preparation of 4,4-difluorohexahydrophthalic anhydride and 4-chloro-4-fluorohexahydrophthalic anhydrides by reaction of hydrogen fluorides with 4-chlorotetrahydrophthalic anhydride.
Skvarchenko et al., Obshchei Khimii, Vol. 30, No. 11. pp. 3535-3541 disclose the aromatization of chloro-substituted tetrahydrophthalic anhydride by heating with phosphorus pentoxide. In the aromatization process described, however, decarboxylation also occurs with the formation of the corresponding chloro-substituted benzene compound. The preparation of various other tetrahydrophthali acids and anhydrides and various methods for dehydrogenation and aromatization thereof are reviewed by Skvarchenko in Russian Chemical Review. Vol 32, Nov. 1963, pp. 571-589.
Co-pending application Ser. No. 405,606, is directed to the preparation of halophthalic anhydrides by the liquid phase reaction of bromine with halotetrahydrophthalic anhydride or gem-dihalohexahydrophthalic anhydride.
The aromatization of organic compounds has been shown in the literature using various techniques and special catalysts. However, it will be apparent to those skilled in the art that a more efficient process for aromatization is desirable.